Multichip free-space global optical interconnection demonstration with integrated arrays of vertical-cavity surface-emitting lasers and photodetectors

The experimental optical interconnection module of the Free-Space Accelerat or for Switching Terabit Networks (FAST-Net) project is described and chara cterized. Four two-dimensional (2-D) arrays of monolithically integrated ve rtical-cavity surface-emitting lasers (VCSEL's) and photodetectors (PD's) w ere designed, fabricated, and incorporated into a folded optical system tha t links a 10 cm x 10 cm multichip smart pixel plane to itself in a global p oint-to-point pattern. The optical system effects a fully connected network . in which each chip is connected to all others with a multichannel bidirec tional data path. VCSEL's and detectors are arranged in clusters on the chi ps with an interelement spacing of 140 Calculations based on measurements o f resolution and registration tolerances showed that the square 50-mu m det ector in a typical interchip link captures approximately 85% of incident li ght from its associated VCSEL. The measured optical transmission efficiency was 38%, with the losses primarily due to reflections at the surfaces of t he multielement lenses, which were not antireflection coated for the VCSEL wavelength. The overall efficiency for this demonstration is therefore 32%. With the measured optical confinement, an optical system that is optimized for transmission at the VCSEL wavelength will achieve an overall efficienc y of greater than 80%. These results suggest that, as high-density VCSEL-ba sed smart pixel technology matures, the FAST-Net optical interconnection co ncept will provide a low-loss, compact, global interconnection approach for high bisection-bandwidth multiprocessor applications in switching, signal processing, and image processing. (C) 1999 Optical Society of America.